It is a never-ending design challenge to reduce power consumption for all types of products. The design challenge is even greater for portable devices such as laptop computers, pagers, cellular telephones, etc. In such devices, power saving techniques are balanced with advanced feature sets that consume power. Typically, the more advance the feature sets that a portable device supports, the more power it consumes. Thus, design engineers of portable devices are constantly working to reduce the power consumption of advanced feature sets with minimal affects on the performance of the feature set.
In general, video graphics circuits, which are utilized in portable computers, personal computers, television sets, and computer game devices, continually process pixel information from video data. This is true regardless of whether the raster is in the active display area (i.e., there is video data to be processed) or when the raster is in an inactive overhead area, which is required for synchronization signals and retrace times. As is known, the video data consists of a plurality of lines, which make up a frame (or field for interlaced display) of video, and may be for two-dimensional graphics, three-dimensional graphics, still images captured by a camera, and/or moving images captured by a camera. One frame/field of video data provides a display screen worth of information for one cycle of the image rate of the display. For example, if the image rate is sixty (60) frames/fields per second, the frame/field is presented for one-sixtieth of a second. The plurality of lines includes the video information (i.e., the information that will be presented on the screen), horizontal retrace, and vertical retrace (i.e., the overhead information). The horizontal retrace is used to provide horizontal synchronization of the video display and the vertical retrace is used to provide vertical synchronization of the video display.
In typical video processing circuits, when the horizontal retrace and vertical retrace are occurring, the pixel generation circuit of the video graphics circuit is still active with a running clock even though no video data will be displayed. Since the horizontal retrace and the vertical retrace account for significant portion of the frame/field time (e.g., up to 25% or more), the pixel generation circuit is overworked by a corresponding percentage. As such, the power consumed by the pixel generation circuit during the horizontal and vertical retraces is wasted energy, resulting in a non-optimum video graphics circuit.
Therefore, a need exists for a method and apparatus that reduces power consumption in video graphics circuitry by selectively disabling the pixel generation circuit.